inflammation of the throat, and loss of appetite. At a more severe dose (viz., usually
greater than 200 rems), the individual will experience bloody diarrhea, fever, bruising (of
the gums in particular), and hair loss. The loss of hair is a good indicator of this level of
exposure. At doses beyond which survival is not usually possible (e.g., greater than
1,000 rems), the degree of development of the above symptoms will be more severe
and will show no signs of dissipation. Death usually occurs during the second or third
week following the exposure.
d. Although the signs and symptoms listed above will apply for the average
human with a uniform exposure, there are several factors that will affect the individual's
response to the radiation. The dose, type of radiation, area exposed, sex, age, and
general health status are each important modifiers of the response. For example,
factors relevant to the bone marrow injury are the dose, quality of the radiation, and the
uniformity of the irradiation. This is a result of the location of the bloodforming organ
within the body. Long bones, the sternum, costals, and cranium are all active sites of
marrow production. Any single area not exposed will normally provide sufficient marrow
reserve. Also, because active sites of marrow production change during development
and aging, age becomes another important determinant. The intestinal lining, a second
site critical for the development of radiation injury, can be affected by a highly localized
dose. For this reason, radiation quality and depth of penetration are important to this
type of injury. X-rays and gamma radiation have great penetrating ability and can affect
e. The dose at which 50 percent lethality occurs is measured and quoted as the
LD 50/30. For most mammals this dose is approximately 500 rems; for humans it is 350
to 450 rems. The outcome for a particular exposure cannot be accurately predicted.
However, the LD 50 (50% of deaths) for man is believed to be somewhere between 200
and 500 rads. This is usually quoted as 450 rads.
1-18. DELAYED SOMATIC EFFECTS OF RADIATION
a. A chronic exposure (as opposed to an acute exposure) is one received over a
long period of time. Frequent occupational exposures or constant irradiation due to
internally deposited isotopes fall within this category. The effects of a chronic exposure
are long range and often difficult to determine; it is difficult to prove that such damage
as cancer, leukemia, life-shortening, and genetic mutations are induced by radiation in
any particular case. Statistical evidence, however, does link damage of this type to
radiation exposures. Long-term effects of this type are not limited to being caused by
chronic exposures; acute radiation exposures may also result in long-term effects.
b. Cancer or carcinogenesis is one long-term effect of radiation. There is a
higher incidence of cancer among those who have received significant doses due to
either chronic or acute exposure to radiation than in persons who have not. By 1922, a
large percentage of the pioneer radiologists suffered from cancer. It is generally
accepted that the probability an individual will suffer from cancer increases
proportionally to his total absorbed dose.